Nuclear reactors structured for use by the power utilities industry are generally configured having a reactor core incorporating fuel in the form of bundled fuel rods or pins, control rods, internal radial blankets, shields and the like. From time to time, the fuel structures are replaced or reoriented by some form of remotely-controlled manipulative mechanism in order to maintain or optimize core performance. Requisite manipulation of the fuel assemblies and components may be carried out employing a variety of techniques, for instance, utilizing a fuel-in-vessel transfer machine (IVTM). For any such manipulation of fuel bundles or assemblies contemplated, however, a form of monitoring or tracking is called for such that the identity, history, position or location and orientation of the fuel assembly is always known. Heretofore, such tracking has been carried out by resorting to carefully maintained historical records or inventory data. This form of tracking may be subject to error and may inject time consuming inefficiencies the refueling process.
Over the recent past, investigators have undertaken the development of a modularized power system utilizing a somewhat standardized reactor module which may be fabricated at a factory location and then transported to a power facility site. The module thus developed was termed a "Power Reactor Inherently Safe Module" referred to by the acronym, PRISM. It is now known as the "Advanced Liquid Metal Reactor" referred to by the acronym ALMR.
In general, the below ground ALMR reactor is a compact pool type in which liquid sodium is circulated through the core by means of four cartridge-type electromagnetic pumps. Core produced heat is transferred from the hot primary liquid sodium via two intermediate heat exchangers performing with an isolated secondary liquid sodium component which is directed without the reactor vessel to a steam generator function. A cylindrical spent fuel storage region also is provided within the primary liquid sodium coolant above the reactor core which incorporates storage racks along its inner surface for carrying out a temporary storage of spent fuel bundles. This storage region also may include rotational devices for use in carrying out fuel bundle reorientation procedures, however, such fuel bundle rotational maneuvering also may be developed with the transfer mechanism itself. The spent fuel from a given cycle is stored at the noted storage region within the reactor and under the surface of the liquid sodium until a next refueling, allowing its decay heat to subside. When the spent fuel subsequently is removed, it then can be handled within inert gas which provides important savings in fuel facilities and fuel handling equipment. Of course, it is important that the fuel bundles positioned at the fuel storage location indeed represent properly spent fuel. Any tracking mistake in the selection of such bundles perforce will lead to an undesired overheating at the storage location, inasmuch as moderators otherwise present at the core region will not be present.
The fuel in-vessel transfer machine (IVTM) used with this reactor is called upon to operate within the primary liquid metal coolant, i.e. "under sodium" and is configured in the manner of a pantograph, the stationary leg of which is supported from a rotatable reactor vessel plug within the upwardly-disposed reactor closure assembly.
In view of the foregoing, it will be highly advantageous to incorporate within a reactor vessel, a capability for carrying out a remote positive identification and a determination of rotational orientation for fuel assemblies while beneath the liquid coolant within the active reactor environment. For facilities such as the ALMR reactor, this requires an "under sodium" identification of fuel assemblies. Such an identification technique will have broad application to conditions requiring tracking or readout within hostile environments, or where conventional codes are readily destroyed in the course of product usage. Environments which may be encountered will include, for instance, radio activity, gas, under-water and the like.